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A Natural History of the Sonoran
Desert, edited by Steven J. Phillips and Patricia Wentworth Comus,
University of California Press in collaboration with the Arizona-Sonora
Desert Museum Press. 1999. ISBN 0-520-21980-5. Paperback, $24.95.Julio L.
Betancourt

It was heartening to read a no-nonsense and comprehensive description
of the natural history of the Sonoran Desert, my home turf for the last
22 years. In my travels across other deserts, I’ve always thought of the
Sonoran as the most unique and diverse, from its varied geologic history
and its 17 indigenous peoples to the many sources and kinds of storms that
create its rain. Among other things, this Mexican-American desert hosts
a phenomenal variety of plants, reptiles and pollinators unrivaled, not
just by other deserts, but by rain forests worldwide.

The editors of this fine volume rely on an impressive pool of local
talent to cover the balance of subjects, from geologic to human history,
from arthropods and mammals, to reptiles and birds. Some of these talented
folks work at the Arizona-Sonora Desert Museum, a wondrous labyrinth of
mostly outdoor exhibits on the west flank of the Tucson Mountains. I would
call Tom Van Devender, for instance, if I wondered when saguaro and palo
verde first appeared in the fossil plant record of southern Arizona. Mark
Dimmitt, who has a heavy hand in this volume, would be my first choice
for queries about the flowering times and life histories of particular
plants. And who better to talk about conservation biology or ethnobotany
of the Sonoran Desert than Gary Nabhan. If my question involved how surface
geology and soils affect local plant distribution, I would not hesitate
to call Joe MacAuliffe of the Desert Botanical Garden in Phoenix. For pollination
ecology, I would get an expert opinion from Steve Buchmann of the Carl
Hayden Bee Lab, who reminds us that of the 5,000 species of bees in North
America, more than 1,000 can be found within 30 miles of Tucson. And for
a philosophical chat about late 19th century Tucson entrepreneurs like
Leopoldo Carrillo, Sam Hughes and L. H. Manning and their landscape-altering
shenanigans, I would go cross-town to my old buddy Tom Sheridan at the
Arizona State Museum.

There is little missing in this book and much to recommend it. Of course,
as with any multi-authored, natural history compendium, it contains occasional
redundancies (desert pavement is explained in two different chapters) and
some unevenness in presentation (the level of sophistication varies in
the additional readings recommended after each chapter). Just the same,
I’ve already recommended the book twice, first to introduce the Sonoran
Desert to a newly hired professor, and again to a visiting sister-in-law.

This book was written to answer many questions, the kinds of questions
that the annual half a million visitors to the Arizona-Sonora Desert Museum
ask each year. In fact, this volume was the logical outgrowth of the Docent
Handbook, a dog-eared compilation of natural history information that,
for more than 50 years, has guided the training of the museum’s world-renowned
volunteer interpreters. Naturally, then, this book showcases a trained
ear for public interest and the trial-and-error experience of effective
explanation to a broad audience. It offers tutorials on photosynthesis,
monsoons and desert mirages, along with Nature-watching tips by month and
locality.

It is also a graphic reminder of the natural wonders that will be lost
if we pave the desert over and unconsciously whittle it down. More than
half of the Sonoran Desert is no longer covered by native vegetation, dominated
instead by 380 exotic plants. I live on Tucson’s north side, arguably one
of the fastest growing metropolitan areas in the United States, wrapping
itself around the scenic Catalina Mountains at an alarming pace. In the
next 20 years, the Sonoran Desert in southern Arizona will be one of the
great staging grounds for retiring baby boomers looking for a warm spot
with a sunset view. Awareness raised by this book and other venues will
determine whether or not these same baby boomers will witness pregnant
bats from Mexico migrating north to feed on the nectar of night-blooming
cacti in May.

Betancourt works in the Desert Laboratory of the U.S. Geological
Survey and University of Arizona in Tucson.

The diverse geological settings of metallic ore deposits and the varied
methods used in assessing their genesis make writing a comprehensive textbook
on ore deposits a formidable challenge. Kula Misra has met that challenge
and produced a first-rate book that reviews the techniques employed in
ore deposit research and summarizes the geological and geochemical characteristics
and origins of selected classes of metallic ore deposits. In a field that
generates new data daily, Understanding Mineral Deposits is up-to-date
and useful.

The book begins with a brief introduction that presents definitions
of a few commonly used terms (e.g., orebody, tenor, reserve or resource)
and reviews principles of ore formation and geochemical tools used to investigate
and interpret processes of ore genesis. For example, the second chapter
covers magmatic, sedimentary, metamorphic and hydrothermal processes of
metal accumulation and ore formation, along with examples of modern or
ancient deposits to illustrate the various processes involved in ore genesis.
Chapters 3 and 4 deal with the application of mineralogical (mineral assemblages,
phase relationships, hydrothermal alteration, paragenesis and zoning) and
geochemical (fluid inclusions, trace elements, stable and radiogenic isotopes)
data to the interpretation of mineral deposits. It also presents the basic
theory underlying the analysis of fluid inclusions, stable isotopic fractionation,
radioactive decay, element distribution and partitioning, phase equilibria,
and textural analysis. The overview of the techniques used in critically
evaluating the genesis of a mineral deposit is complete and focused and
illustrates the steps a graduate student might logically follow in dissertation
research. The 236 pages devoted to this section would be an essential component
of an upper-level university course in metallic mineral deposits.

The second part of the book describes various types of ore deposits.
Misra has done an excellent job of summarizing the wealth of literature
that now exists for virtually all deposit types. He covers chromite, Ni-Cu
sulfides, PGE, porphyry Cu-Mo-Sn, skarns, volcanic-associated massive sulfides
(VMS), sediment-hosted massive Pb-Zn (SMS), sediment-hosted stratiform
Cu (SSC), Mississippi Valley Type Pb-Zn (MVT), uranium, Precambrian iron
formations, and gold. Although not all chapters are organized in exactly
the same manner, the general scheme is to review the distribution and types
of deposits within the overall class, present a series of examples of well-studied
deposits, discuss the composition of the ores and their metallogenesis,
summarize distinguishing characteristics and favored theories of origin,
and give a short list of recommended readings. The discussions of the similarities
and differences between deposit types, some that are often confused, are
especially informative. For example, Misra discusses the distinctions between
VMS, SMS, SSC and MVT deposits in a comparison following the MVT chapter.
The chapters on uranium and banded iron formations include well-organized
discussions on the development of Earth’s early atmosphere. An overview
of the origin of gold in the conglomerates of the Witwatersrand Basin is
included in the chapter on uranium. Readers should appreciate the detailed
discussions of the possible origins for all of the deposit types and the
vast amount of data upon which these evaluations are based.

Space limitations mean that some topics, particularly those covered
in the first part of the book, cannot be treated in the detail that is
often necessary for a thorough understanding of the principles involved.
For example, accompanying text in advanced geochemistry would be required
for a more complete treatment of all of the topics reviewed in chapters
2 through 4. Such a problem is inherent to most courses on ore genesis
and to almost any economic geology textbook. Misra has at least provided
the references that an interested reader would need for a more in-depth
explanation of the foundations that underlie geochemical principles.

The length of the book reflects an increased knowledge base, and the
likelihood that all of the information presented can be covered in a one-semester
university course is small. Kula Misra states in the preface that a class
in mineral deposits should be a capstone course that draws on concepts
from several areas in geology. With this book he has succeeded in highlighting
the multidimensional nature of economic geology. It is also an excellent
reference for professional geologists and a useful text for a senior- or
graduate-level course in metallic mineral deposits.

Ripley teaches in the Department of Geological Sciences at Indiana
University, Bloomington.

Edward Drinker Cope (1840-1897) and O.C. Marsh (1831-1899) were the
most prominent American paleontologists of the 19th century. Collectively,
Cope, Marsh, and their hired collectors exhumed a staggering number of
vertebrate fossils, mostly in the western United States. These were busy
guys. Marsh published about 300 scientific papers on vertebrate fossils
during his career, and he had as many as seven collecting parties in the
field at one time. Cope published nearly 1,400 scientific papers in his
career — 76 papers in 1880 alone, a rate of one paper every 4.8 days.

Despite some spectacular discoveries and their enormous contributions
to paleontology, Cope and Marsh are best known today for sloppy taxonomy
and anatomical blunders, and for feuding with each other. They were bitter
rivals who often competed for the same fossil-rich deposits. Surrounding
them are stories of spies and counterspies, stealing each others’ fossils
and smashing bones in the outcrop to prevent the other guy from getting
them. Wallace aptly refers to this style of field work as “smash-and-grab
paleontology.” He includes a quote by paleontologist Bjorn Kurten that
captures the ambivalence one feels for Cope and Marsh: They “transformed
paleontology [into] a dynamic science and charged it with a spirit of discovery.
At the same time, the rivalry and enmity between these two eminent scientists
is a dark chapter in the history of paleontology.”

The Bonehunters’ Revenge is the first book-length treatment of
the Cope-Marsh affair since Elizabeth Noble Shor’s 1974 book, The Fossil
Feud between E.D. Cope and O.C. Marsh. The feud has lately become a hot
topic: another Cope-Marsh book, The Gilded Dinosaur by Mark Jaffe, was
published this year, and a biography of Cope, The Bone Sharp by J.P. Davidson,
was published in 1997.

The Bonehunters’ Revenge is essentially a double scientific biography,
alternately tracking the lives and careers of Cope and Marsh, emphasizing
their interactions and influences on each other. It is a carefully researched,
well-written account of a fascinating and disturbing episode in the history
of American science.

Wallace is a writer-historian with no prior professional experience
with paleontology or the history of geology, but he did his homework and
fieldwork for this book. He spent time digging horse fossils with Greg
McDonald at Hagerman Fossil Beds National Monument in Idaho, for example,
and he explored the San Juan Basin (where Cope discovered the first-known
Paleocene fauna) with Spencer Lucas of the New Mexico Museum of Natural
History and Science. Endnotes and citations allow the interested reader
to easily pursue selected topics in greater detail.

Wallace’s most significant contribution to the literature on the Cope-Marsh
fossil feud is his insightful exploration of the role of the press. The
book begins with a lengthy prologue about James Gordon Bennett Jr., owner
and publisher of the New York Herald from 1868 to 1918. The Herald transformed
the antagonistic relationship between Cope and Marsh from a private feud
into a public spectacle. In January of 1890, Bennett’s newspaper published
a splashy exposé of Marsh (the vertebrate paleontologist of the
U.S. Geological Survey at the time) and John Wesley Powell (then the survey’s
director). This article, written by a Cope confidant, was followed by multiple
rounds of published responses and countercharges by Marsh and Powell, no-holds-barred
attacks by Cope, and accusations and refutations by several other paleontologists
who were sucked into the fracas. Wallace portrays Bennett as the cynical
puppet master who manipulated the naïve scientists into airing their
dirty laundry in public so that he could sell newspapers.

In general, Wallace deserves high marks. His book reveals the way in
which North America’s vertebrate fossil record was discovered, how it contributed
to the elucidation of the history of vertebrate groups generally, and how
important the newspapers were in popularizing paleontology in the late
19th century. On the other hand, the complete absence of maps and the general
paucity of illustrations were frustrating. I have not visited most of the
fossil localities described in the book, and I wanted to get a better feeling
for the rocks and fossils than the book provides. There are several photographs
of people and a few period cartoons and sketches, but not nearly enough
illustrations of fossils and strata to suit me. It’s a good story well
told if not well illustrated.

Rowland teaches in the Department of Geosciences at the University
of Nevada, Las Vegas.

Software

Contouring Explained

By Betty L. Gibbs and Stephen A. Krajewski

Free Poster! A
free contouring poster -- coming in the December print issue of Geotimes
-- will contain more details on computer contouring using five common methods:
Triangulation, Inverse Distance Weighting, Ordinary Kriging, Minimum Curvature
and Trend Surface.

Contouring: The construction of lines (contours) connecting points
of equal elevation on a map representing topography.Glossary of Geology, fourth edition

For decades, geoscientists performed contouring of irregular spatial
data by hand. Computer contouring started on mainframe computers in the
1950s but has become more widely used in the earth sciences since the advent
of microcomputers in the early 1980s. Stand-alone contouring programs can
be obtained from several public domain sources at no cost. Commercial programs
range in price from $500 to tens of thousands of dollars, but enough inexpensive
hardware and software is available that computer contouring is affordable
for almost anyone.

Contours are a graphical display of spatial data relationships that
help us to “see” where we cannot be. Whether the contours represent the
top of a geologic formation or a quality value such as porosity or sulfur
content, the contour lines are an interpretation of the data made by hand
or with computer software. On the other hand, contours of surface topography
show lines of equal elevation, closely approximate a surface and are definable
from aerial photos or ground surveys. Contouring is also an art and the
geologist uses available tools — whether the tool is a pencil or a computer
— to produce a map that most accurately represents spatial data according
to the expert’s experience, vision and perception. But even with computer
contouring, uncertainty remains in knowing or proving that the contours
truly represent the surface or values.

In general, making contour maps is easy. By hand, the process is slow
and tedious but allows the easy addition of interpretations based on geological
knowledge. Making contour maps with a computer is much faster, but the
user has less direct control over how contours look than with hand contouring.
Whether simple or sophisticated, gridding and contouring software is flexible
enough to satisfy almost any contouring need with speed and convenience.
Computer contouring is based on mathematical algorithms and is therefore
not a perfect representation of data. It is necessary to constantly check
results for errors and to make sure the contours are representative of
the data. To produce the best possible contour maps, the geologist or engineer
must know the software’s limitations and which contouring methods are most
likely to produce an acceptable result. They must also be willing to experiment
with different methods.

A person who does contouring by hand is usually confident in the interpretation
and result. However, it has been proven many times that different people
interpret a set of data in different ways — so what is a “correct” result?
Surface contours are easy to check in the field. But contours representing
an underground geologic formation’s structure or representing quality values
are made by interpreting and estimating possible values between data points.
Verifying such interpretations may prove impossible, costly or too destructive.
The best defense against possible contouring errors is a clear understanding
of contouring methods and their limitations, as well as a willingness to
experiment, question results, and add reasonable interpretation when necessary.

A contour map constructed on a computer is too often considered a “true
representation” of the actual surface with little or no error. How close
the contouring method is to reality is rarely questioned. The mathematical
world of the computer imposes a fixed interpretation on data derived from
the random processes of Nature. Computerized contour maps should be examined
and questioned and accepted only after many trials with different selections
of control parameters.

Contouring errors (“noise” or artifacts) are introduced by selecting
the wrong estimation method or algorithm or by incorrectly specifying the
mathematical controls that dictate how the algorithm is applied to spatial
data. Some contouring methods produce more artifacts than others, but most
artifacts can be eliminated with proper selection of the control parameters.
Recognizing potential errors in both manual and computer methods, and adjusting
those methods when need be, is essential to produce a truly representative
contour map.

Gibbs is president of Gibbs Associates in Boulder, Colo., and is
a mining engineer with more than 30 years experience working for mining
companies and as a consultant. E-mail: bgibbs@csn.org

Krajewski, a geographer and geologist, is chief geologist for Industrial
Ergonomics Inc. in Arvada, Colo., which provides training and consulting
services. He also works with geographic information systems for the city
of Loveland, Colo. E-mail: iei@uswest.net

ourworld.compuserve.com/homepages/eworks/The Earthworks Web site offers job listings posted by employers in
a multitude of earth-science fields from around the world. Browse listings
in environmental science, postgraduate courses, soil science, geotechnical
engineering, petroleum engineering and many other fields. Job seekers can
post resumés on the site and employers can search the catalog of
resumés for potential employees.